Who, when they were come down, prayed for them, that they might receive the Holy Ghost:

Note 2 at Ac 8:15: It is not explained in this instance why Philip did not pray for these new converts to receive the Holy Ghost. Some people have argued that only the apostles had the power to give the Holy Ghost to others, and therefore Philip was unable to do so. However, we see in Ac 9:10-18, Ananias, who was just a disciple at Damascus, was the instrument God used to give the Holy Ghost to Saul. So believers other than apostles were able to lay hands on people and have them receive the Holy Spirit.